Iron Isotope Systematics of the Skaergaard Intrusion and Implications for its Liquid Line of Descent.

This article focuses on the iron (Fe) isotope systematics of the Skaergaard intrusion, a well-studied layered mafic intrusion in East Greenland, to elucidate its magmatic differentiation and liquid line of descent (LLD). New Fe isotope data from whole rocks and FeTi oxide minerals reveal variations in δ⁵⁶Fe values that correlate with mineralogical changes, particularly the appearance of magnetite, and suggest that fractional solidification in a (near) closed system controls Fe isotope evolution. Modeling of Fe isotope fractionation using Fe²⁺ and Fe³⁺ force constants supports an intermediate LLD between classic Fenner (Fe enrichment with little silica increase) and Bowen (silica enrichment with Fe depletion) trends, requiring a modest (~3.5%) residual felsic liquid after solidification consistent with observed granophyres. The study finds no resolvable effects of liquid immiscibility, crustal contamination, hydrothermal alteration, or thermal diffusion on Fe isotopes at the bulk rock scale, and concludes that Fe isotope variations primarily reflect fractionation of Fe-rich minerals during magmatic differentiation, providing insights complementary to volcanic records.